The present invention relates to a dynamic-pressure type hydrodynamic bearing device and a spindle motor using the same.
A hydrodynamic bearing comprises a shaft and a sleeve for supporting the shaft, and a lubricant is filled in a clearance where the two are opposed to each other. As the shaft rotates, the lubricant is scraped up and pressure is generated by dynamic pressure generation grooves formed on the shaft or the sleeve, and the shaft is supported without making contact with the sleeve. Hence, high-speed rotation can be realized, and noise generated during rotation can be reduced.
Since spindle motors incorporating these hydrodynamic bearing devices are excellent in rotation accuracy indispensable for achieving higher recording density of media and also excellent in impact resistance and quietness, they have become the mainstream of motors for use in information equipment typified by magnetic disk apparatuses and in audiovisual equipment. For this reason, in recent years, from the viewpoint of miniaturization and energy conservation of equipment, the motor current consumption of the spindle motor, more particularly, the torque of the hydrodynamic bearing device, significantly affecting the motor current consumption, is strongly requested to be reduced.
Since the resistance torque of the hydrodynamic bearing device is proportional to the viscosity of a lubricant to be applied, the use of a lubricant having lower viscosity is effective in reducing the resistance torque.
In addition to conventional hydrodynamic bearing devices that use dioctyl sebacate (DOS), dioctyl azelate (DOZ), dioctyl adipate (DOA), etc. as lubricants, a hydrodynamic bearing device (Japanese Laid-open Patent Application 2000-336383) that uses the mixed esters of neopentyl glycol caprylate and neopentyl glycol caprate, a hydrodynamic bearing device (Japanese Laid-open Patent Application 2001-316687) that uses an ester obtained from neopentyl glycol and a monovalent fatty acid having 6 to 12 carbon atoms and/or its derivative, a hydrodynamic bearing device (Japanese Laid-open Patent Application 2002-195252) that uses a polyol ester derived from a diol component having an alkyl side chain at the β position or the β and β′ positions, etc. have been proposed.
However, in these conventional examples of hydrodynamic bearing devices, although the torque can be reduced, such problems are caused that the amount of evaporation of the lubricant increases since the heat resistance of the lubricant is low, the service life of the device is shortened, and the reliability of the device cannot be obtained sufficiently. In addition, in the case that a more than necessary amount of the lubricant is applied in consideration of the amount of evaporation of the lubricant, such problems are caused that increase in torque and increase in cost are caused corresponding to the amount, and miniaturization becomes difficult since it is necessary to obtain space.
In consideration of the problems described above, the present invention is intended to provide a hydrodynamic bearing device being low in torque, low in power consumption, high in reliability and best suited for miniaturization and a spindle motor using the same by using, as the lubricant of the hydrodynamic bearing device, a lubricant containing diesters obtained from a divalent alcohol having 4 to 8 carbon atoms and having no alkyl side chain at the β position and one or more kinds of saturated monovalent fatty acids having 9 to 13 carbon atoms.